If an automobile collides against another automobile, a building, etc., a driver of the automobile collides with a steering wheel by its inertia (which will hereinafter be termed a secondary collision in the present specification) in some cases. Cars, etc. in recent years have widely adopted an impact absorption type steering column apparatus in order to prevent the driver from being injured in such a case. In the impact absorption type steering column apparatus, when the driver secondarily collides with the steering wheel, the steering column separates from a the car body together with a steering shaft or the steering column becomes collapsed simultaneously with the steering shaft, whereby an impact energy is absorbed on that occasion.
Some of the impact absorption type steering column apparatuses have an impact energy absorption system that absorbs the impact energy by causing a flexural deformation of a car body securing bracket for securing the steering column to the car body.
Such an example is disclosed in Japanese Patent Publication No. 2978788 and Japanese Patent Application Laid-Open Nos. 2000-229577 and 10-16796. FIG. 7 shows one example of the conventional impact absorption type steering column apparatus. A tilt adjustment type steering column a is so secured to the car body as to be tilt-adjustable through a car body securing bracket (tilt bracket) b and has substantially an L-shape when viewed from its side.
This car body securing bracket b with substantially the L-shape as viewed from its side is constructed of a car body securing portion c for securing it to the car body by use of a bolt, etc., a support wall portion e bent substantially in an L-shape through a bent portion d from this car body securing portion c, and a column fastening fixation portion g erected from this support wall portion e formed with a tilt adjustment groove f.
A distance bracket h fixed by welding, etc. to the steering column a is slidably provided inside the car body securing bracket (the tilt bracket) b, and a fastening bolt i is inserted through the tilt adjustment groove f of the column fastening fixation portion g and through the distance bracket h. A fastening lever j fitted to a proximal end portion of this fastening bolt i is swayed towards a driver on the rear side of the vehicle, thereby fixing the car body securing bracket b to the distance bracket h by pressing. Then, the fixation by press-fitting can be canceled by rotating the fastening lever j in the opposite direction.
In the examples disclosed in the Publications of the prior art and in the conventional example in FIG. 7, the bent portion d and the support wall portion e are disposed at the front side of the vehicle on the car body securing portion c, and the column fastening fixation portion g formed with the tilt adjustment groove f is disposed at the rear side of the vehicle on this support wall portion e.
Accordingly, when a secondary collision happens, a secondary impact load acts towards the front from the rear of the vehicle, with the result that the steering column a is forced to move toward the front of the vehicle together with the distance bracket h and the fastening bolt i. On this occasion, the fastening bolt i starts moving, as indicated by an arrowhead (k) in FIG. 7, with the bent portion d serving as a fulcrum, in a direction considerably downwards from the horizontal direction and subsequently, as indicated by an arrowhead (k) in FIG. 7, rotates about the bent portion d. With this action, the support wall portion e of the car body securing bracket and the column fastening fixation portion g become collapsed while causing their flexural deformations so as to rotate about the bent portion d (fulcrum), thereby absorbing an energy of the secondary impact.
In the examples disclosed in the Publications of the prior art and in the conventional example in FIG. 7, however, the bent portion d and the support wall portion e are disposed at the front side of the vehicle on the car body securing portion c, and the tilt adjustment groove f and the column fastening fixation portion g are disposed at the rear side of the vehicle on this bent portion d and the support wall portion e. Therefore, when the secondary collision happens, the fastening bolt i (the support wall portion e of the car body securing bracket b and the column fastening fixation portion g) starts moving, as indicated by the arrowhead (k) in FIG. 7, in a direction of rotating about the bent portion d as a fulcrum, and this direction is considerably downward from the horizontal direction.
On the other hand, the steering column a is secured to the actual car at a tilt angle of approximately 20 through 24 degrees, however, when the secondary collision happens, the impact load on the driver acts substantially horizontally towards the front from the rear of the vehicle.
Accordingly, there is a considerable deviation between the input direction (substantially the horizontal direction) of the impact load and the actual motion starting direction (downward) of the fastening bolt i (the support wall portion e of the car body securing bracket b and the column fastening fixation portion g). As a result, the start of motions of the fastening bolt i and the car body securing bracket b are not necessarily stable.
Further, in the conventional example shown in FIG. 7, the fastening lever j extends at the rear side of the vehicle in the state where the steering column a is fixed in the tilt adjusting position, and hence this fastening lever might, when the support wall portion e of the car body securing bracket b and the column fastening fixation portion g rotate about the bent portion d (fulcrum) upon the secondary collision, fall down, following up these rotations, from an accommodation area within the steering column a and might be positioned in the vicinity of a knee of the driver.
Japanese Patent Application Laid-Open No. 10-16796 takes a countermeasure against this incident, wherein the apparatus is structured to prevent the fastening lever from rotating when the secondary collision happens. This mechanism is, however, complicated requiring an increase in the number of parts, with the result that a rise in the manufacturing cost is brought about.